Method of metal plating with a group iv-b organometallic compound



United States Patent 3,061,464 METHOD OF METAL PLATING WITH A GROUP IV-BORGANOMETALLIC COMPQUND Vello Norman and Thomas P. Whaley, Baton Rouge,La.,

assignors to Ethyl Corporation, New York, N.Y., a corporation ofDelaware N0 Drawing. Filed Oct. 9, 1959, Ser. No. 845,306

9 Claims. (Cl. 117-1t)7) This invention relates to a process for platinggroup IV-B metals of the periodic chart of the elements on appropriatesubstrates by decomposition of organometallic compounds of such metals.

A simplified flow diagram of the process of this invention is asfollows:

Substrate Heat to decomposition temperature of a monocyclopentadienylgroup IV-B transition metal coordination compound Contact heatedsubstrate with vapors of the above compound Cool In the past, processesfor the preparation of a group IV-B metal plateparticularly titanium andzirconium plates-have been limited to impractical high temperatureprocesses. Illustrative of these high temperature prior art processesare thermal decomposition of titanium or zirconium iodides at 1200 to1500 C. and hydrogen reduction of titanium tetrachloride and titaniumtetrabromide at 1100 to 1400 C.

Plates produced by prior art reduction methods are unsatisfactory fortwo major reasons. The first of these is that the resultant metal plateis of poor quality due to hydrogen embrittlement. It is well known thattitanium and zirconium are particularly susceptible to hydrogenadsorption and this results in the preparation of poor quality hydrogenembrittled metal plates. The second deficiency is that metal platesproduced by these prior art methods have poor adherence to the surfaceon which the metal is plated.

A further problem accompanying prior art processes is the necessity forexcessively high temperatures. Furthermore, the plating agents utilizedin these prior art processes (e.g. iodides or bromides of titanium orzirconium) are very reactive and also very difficult to purify. Becauseof their reactivity these plating agents are likely to react with theconstituents of the atmosphere. When the plating agent, containing theseconstituents as an impurity, is subsequently introduced into the platingatmosphere, undesirable embrittlement of the plate results.

In addition to the above methods, electroplating from fused salt bathshas been employed as a technique for producing group IV-B metal plates,particularly titanium plates. However, one of the foremost problemsrelative to this technique is that the plate is deposited thinly andunevenly, or dendritically. Thus, in short, there is no knownsatisfactory process for producing group -IVB metal plates.

Titanium and zirconium metal plates are highly desirable because oftheir high corrosion resistance and good temperature stabilitycharacteristics. Carbides of these metals are also highly desirable,since these materials are "ice extremely hard, high temperatureresistant compounds. Heretofore, in producing coatings of hard carbides,ithas been necessary to employ temperatures of about 1200f C. in areduction process utilizing a mixture of the metal halide, hydrogen andhydrocarbons.

In view of the foregoing, the novelty and great importance of theinstant invention becomes clear. For the first time, employing theprocess of this invention, it is possible to produce-at temperaturessignificantly below those described above-a well-adhering, pure groupIV-B metal plate. Furthermore, by a simple variation in the process, itis possible to produce the carbide of the corresponding metalssaidcarbide being of excellent characteristics and well-adhering to thesubstrate upon which it is coated. To the best of our knowledge, this isthe first time that such plating processes have been employed inproviding group IV-B metal plates.

It is, therefore, an object of this invention to provide a process forthe preparation of group IV-B metal plates. It is a further object ofthis invention to produce a welladhering, excellent group IV-B metalplate. A still further object of this invention is to produce a groupIV-B carbide coating which has good adherence to the substrate uponwhich deposited.

These and other objects are accomplished in accordance with thisinvention by providing a process for plating a substrate with a groupIV-B transition metal by the decomposition of a monocyclopentadienylgroup IV-B transition metal coordination compound in contact with saidsubstrate. (The group IV-B transition metals are titanium, zirconium andhafnium, e.g. see the periodic chart of the elements, Fisher ScientificCompany, 1955.)

By the term cyclopentadienyl, which is a substituent in theaforementioned coordination compound, is included substitutedcyclopentadienyl groups. The cyclopentadienyl moiety, therefore,includes alkyl and aryl substituted cyclopentadienyl groups as well asindenyl and fiuorenyl derivatives including substituted indenyl andfluorenyl derivatives. The term cyclopentadienyl preferably includeshydrocarbon cyclopentadienyl groups containing S to about 17 carbonatoms.

Alternatively the monocyclopentadienyl group IV-B coordination compoundsof this invention can be defined as mono-(hydrocarbon cyclomatic) groupIV-B coordination compounds. The term cyclomatic hydrocarbon includescyclomatic hydrocarbon radicals having from about 5 to about 17, ormore, carbon atoms and embodying a group of 5 carbons having theconfiguration found in cyclopentadiene. Such cyclomatic hydrocarbongroup lV-B coordination compounds are further characterized in that thecyclomatic hydrocarbon radical is bonded to the group IV-B metal, bycarbon to metal bonds, through the carbons of the cyclopentadienyl groupcontained therein.

The mono-cyclopentadienyl group IV-B transition metal coordinationcompound can be represented by the illustrative formula RMQ wherein Rrepresents a cyclepentadienyl moiety containing a S-carbon n'ng, similarto that contained in cyclopentadiene itself, coordinated to the groupIV-B transition metal, M, through the carbon atoms of thecyclopentadienyl ring; Q represents an electron donor group or acombination of separate electron donor groups, which can be the same ordiflerent from each other, involved in covalent or coordinate-covalentbonding with the metal atom, x has a value of 0 to 4--'and usually 0 to2. These group IV-B coordination compounds will bemore fully definedhereinafter.

By decomposition, as used herein, is meant any method feasible fordecomposing a monocyclopentadienyl IV-B transition metal coordinationcompound. Thus, the

term includes decomposition by ultrasonic frequency and decomposition byultraviolet irradiation, as well as thermal decomposition. Thermaldecomposition is a preferred mode of carrying out the invention.

Therefore, within the scope of this invention, is a process for platinga substrate with a group IV-B transition metal comprising heating thesubstrate to be plated to a temperature above the decompositiontemperature of a monocyclopentadienyl group IV-B transition metalcoordination compound, and thereafter contacting said coordinationcompound with said heated substrate.

Examples of the monocyclopentadienyl group IV-B transition metalcoordination compounds employed in this invention are: cyclopentadienyltitanium trichloride, cyclopentadienyl zirconium trichloride,cyclopentadienyl titanium dibutoxy chloride, cyclopentadienyl titaniumdiethoxy bromide, cyclopentadienyl zirconium di-methoxy chloride,cyclopentadienyl titanium butoxy dichloride, methyl cyclopentadienyltitanium trichloride, indenyl titanium trichloride, fiuorenyl zirconiumtrichloride, cyclopentadienyl hafnium trichloride, cyclopentadienylhafnium di-butoxy chloride, cyclopentadienyl hafnium tribromide, methylcyclopentadienyl hafnium triastatine, octylcyclopentadienyl titaniumtriiodide and the like.

In general, any prior art technique for metal plating an object bythermal decomposition of a metal-containing compound can be employed inthe present plating process as long as a monocyclopentadienyl group IV-Bcoordination compound is employed as the plating agent (i.e., themetallic source for the metal plate). For example, any techniqueheretofore known for the thermal decomposition and subsequent plating ofmetals from the corresponding metal carbonyl can be employed.Illustrative are those techniques described by Lander and Germer,American Institute of Mining and Metallurgical Engineers, TechnicalPublication No. 2259 (1947). Usually, the technique to be employedcomprises heating the object to be plated to a temperature above thedecomposition temperature of a metal-containing compound and thereaftercontacting the metal-containing compound with the heated object. Thefollowing examples are more fully illustrative of the process of thisinvention.

In Examples I-IV the following technique is used:

Into a conventional heating chamber housed in a resistance furnace andprovided with means for gas inlet and outlet, is placed the object to beplated. The organometallic plating agent is placed in a standardvaporization chamber provided with heating means, said vaporizationchamber being connected through an outlet port to the aforesaidcombustion chamber inlet means.

For the plating operation, the object to be plated is heated to atemperature above the decomposition temperature of the organometallicplating agent, the system is evacuated and the organometallic compoundis heated to an appropriate temperature where it possesses vaporpressure of up to about millimeters. In most instances, the process isconducted at no lower than 0.01 mm. pressure. The organometallic vaporsare pulled through the system as the vacuum pump operates, and theyimpinge on the heated object, decomposing and forming the metalliccoating. In most instances, no carrier gas was employed; however, incertain cases, a carrier gas can be employed to increase the efliciencyof the above disclosed plating system. In those cases where a carriergas is employed, a system such as described by Lander and Germer, page7, is utilized.

Example I Compound C H TiCl Substrate Temp 400 C. Substrate Pyrex.Pressure 1mm. Compound Temp 200 C. Time (Hours) 2. Result Shiny,metallic coating.

4 Example II Compound C H ZrCl Substrate Temp 400 C. Substrate Pyrexfibers. Pressure 0.1 mm. Compound Temp 120 C. Time (Hours) 2. ResultShiny, metallic coating Example Ill Compound C5H5(C4HQO)ZTIBI'.Substrate Temp 300 C. Substrate Graphite. Pressure 0.5 mm. Compound TempC. Time (Hours) 1. Result Grey coating.

Example IV Compound Indenyl(butoxy) '1"iBr. Substrate Temp 300 C.Substrate Copper mesh. Pressure 0.2 mm. Compound Temp C. Time (Hours) 2.Result Dull, grey coating.

In the above examples, the temperatures utilized (i.e., in the vicinityof 250-400 C.) gave excellent metal plates. The process employedresistance heating. In the following working examples an inductionheating method, using higher temperatures (i.e., greater than 650 C.)was employed. In the latter process, titanium and zirconium carbidecoatings of excellent characteristics were obtained as opposed to themetallic coatings obtained in the foregoing examples.

The process employed in these examples is essentially the same as thatemployed in Examples I through IV with the exception that the object tobe plated was placed into a conventional heating chamber provided withmeans for high frequency induction heating as opposed to the formerprocess where the heating chamber was housed in a resistance furnace.

Example V Compound C H TiBr Substrate Temp 650700 C. Substrate Ni-coatedmild steel. Pressure 0.2 mm. Compound Temp 125 C. Time (Hours) 1%.Result Dark, shiny, hard, welladherent coating.

Example VI Compound C H ZrBr Substrate Temp 650700 C. SubstrateNi-coated mild steel. Pressure 0.5 mm. Compound Temp C. Time (Hours) 1%.Result Dark, shiny, hard, welladherent coating.

In addition to the thermal techniques disclosed hereinabove fordecomposing the group IV-B plating agents of this invention, othermethods for decomposition of these materials can be employed. Thus, thefollowing working example is illustrative of the decomposition of atitanium compound by ultrasonic frequency.

The process employed in Examples V and VI is followed with the exceptionthat an ultrasonic generator is proximately positioned to the platingapparatus. In this example the compound was heated to its decompositionthreshold, i.e. in the vicinity of 200 C. and thereafter the ultrasonicgenerator was utilized to effect final decomposition.

Example VII Method Thermal and ultrasonic decomp.

Compound C H TiF Compound Temp 150 C.

Substrate Pyrex fibers.

Substrate Temp 200 C.

Pressure 0.1 mm.

Result Metallic coating.

Another method for decomposing the plating agent of this invention is bydecomposition with ultraviolet irradiation. The following example isillustrative of this technique.

The method of Example I was employed, with the exception that, in placeof the resistance furnace, there was utilized for heating a battery ofultraviolet and infrared lamps placed circumferentially around theoutside of the heating chamber. The substrate to be heated was broughtto a temperature just below the decomposition temperature of the platingagent with the infrared heating and, thereafter, decomposition waselfected with ultraviolet rays.

Example VIII Method Thermal and ultraviolet de'comp.

Compound CH C H ZrBr Compound Temp 90 C.

Substrate Aluminum.

Substrate Temp 200 C.

Pressure 1 mm.

Result Grey metallic coating.

The term substrate, as employed hereinbefore, can be defined further asthe object to be plated and includes any material stable at thetemperatures necessary for decomposition of the group IV-B transitionmetal coordination plating agent employed. Illustrative of varioussubstrates are Pyrex glass and spun glass; various synthetic fibers andplastics such as polytetrafluoroethylene, polychlorotrifluoroethylene,rayon, nylon, Delrin (polyformaldehyde resin) and the like; steelsuch asnickel plated steel, mild steel, nickel plated mild steel; metallicturnings such as copper, zinc, and the like, cellulose materials such ascotton, paper, and the likein short, any materials stable under theplating conditions employed.

It should be noted that when employing the novel organometallic platingagents of this invention, it is necessary to maintain enough vaporpressure, below the decomposition temperature of the organometallic, toenable the process to be conducted at an appreciable rate of plating.Too high vapor pressure results in somewhat inferior substrateadherence. Thus, it is preferred to employ up to about mm. pressureduring the plating operation-preferably 0.01 to 10 mm. pressure.

As has already been pointed out, temperatures are very important inobtaining the desired plated product. Thus, although temperatures abovethe decomposition temperature of the monocyclopentadienyl metalcoordination compound can, in general, be employed in the platingprocess of this invention, best results have been attained withincertain preferred temperature ranges. For example, temperatures rangingfrom about 280 C. to about 450 C. produce relatively pure metal platedproducts and temperatures in the range of about 650 C., or above,produce carbide-containing products when the chlorides of themonocyclopentadienyl titanium compounds are employed. The platingcompounds of the present invention vary insofar as their thermalstability is concerned, but all of. them can be decomposed at atemperature above 400 C., and some as low as 100 C. Generally,decomposition occurs above 400 C. when employing chloride derivatives ofthe group IV-B cyclopentadienyl transition metal composition. Othermaterials, such as the bromides, decompose at lower temperatures (e.g.about 300 (3.). The maximum temperatures which are employed are around700 to 750 C.

In one embodiment of the instant invention, mixtures ofmonocyclopentadienyl group IV-B coordination compounds containingdifferent metals are employed in the plating process to produce alloysof the respective metals upon appropriate substrates. An example of thisembodiment is the utilization of cyclopentadienyl titanium trichlorideand cyclopentadienyl zirconium t'richloride as plating agents in aprocess similar to that used in Examples IIV. The following example morefully demonstrates this embodiment.

Example IX Method Thermal decomposition as in Ex. I.

Composition An equimolar mixture of cyclopentadienyl titaniumtrichlori'de and cyclopentadienyl zirconium trichloride.

Composition Temp.-. C.

Substrate Aluminum.

Time (Hours) 1.

Substrate Temp 450 C.

Pressure 0,7 mm.

Result Metallic coating.

The cyclopentadienyl substituents of the group IV-B transitioncoordination compounds, employed as plating agents in this invention,have previously been defined as substituted or unsubstitutedcyclopentadienyl moieties. More specifically, these moieties have beendefined as cyclopentadienyl moieties containing a five carbon ringsimilar to that contained in cyclopentadienyl itself. In most cases thecyclopentadienyl moiety contains from 5 to about 15 carbon atoms.Illustrative of these cyclopentadienyl moieties are cyclopentadienyl,l-methyl cyclopentadienyl, 2-(o-tolyl)-cyclopentadienyl, indenyl, 2-methylindenyl, 3-phenyl-inde'nyl, fiuorenyl, 3-'e'thyl-fluorenyl,2-m-tolyl-tfluorenyl, and the like cyclopentadienyl containing moieties.The cyclopentadienyl radical can alternatively be considered as acyclomatic radical such as 4,5,6,7-tetrahydroindenyl,1,2,3,4,5,6,7,8-octahydrofluorenyl, 3-methyl-4,5,6,7-tetrahydroindenyl,and 2-ethyl- 3-phenyl-3,4,5,6,7-tetrahydroindenyl.

The con'stitutents represented by Q in the above formula are electrondonating groups capable of coordinating with the group IV-B metal atomin the compounds which are employed as plating agents in the process ofthis invention. Thus the groups represented by Q in the above formulaare capable of sharing electrons with the metal atom so that the metalachieves a more stable structure by virtue of such added electrons.These electron donating groups in coordination with the metal are,generally, either organic radicals or molecular species which containlabile electrons. These electrons assume a more stable configuration inthe molecule when associated with the metal. The electron donating grouprepresented by Q may also be inorganic entities which are capable orexisting as ions, such as 'hydro'gen, the cyanide group, and the varioushalogens. In general, the electron donating groups represented by Q arecapable of donating from 1 to 4 electrons. The halogens arerepresentative of electron donating groups donating one electron andcarbonyl illustrative of an entity donating two electrons. An entitydonating three electrons is represented by the nit'rosyl group andaliphatic diolefins are illustrative of entities capable of donatingfour electrons. In those compounds which are preferred plating agents inthe process of this invention, Q represents electron donating entitiescapable of donating one electron. Such entities are the halides such aschlorine, bromine, fluorine, iodine, and the like, and alkoxy andaryloxy groups. Of these it is most preferred that Q be chlorine,bromine, butoxy, propoxy, ethoxy, and methoxy groups.

The group IV-B metals which form the metallic constituent of acoordination compound of this invention include the metals titanium,zirconium and hafnium. Of these, titanium and zirconium are preferredbecause of their greater availability and excellent chemical andrefractory properties. The most preferred metal is titanium because ofits wide adaptability to a multitude of uses.

The following compounds more fully illustrate the types of group IV-Btransition metal coordination compound which can be employed as platingagents in this invention. These compounds are methyl cyclopentadienyltitanium trichloride, methyl cyclopentadienyl titanium tribromide,methyl cyclopentadienyl titanium trifluoride, methyl cyclopentadienyltitanium triiodide, methyl cyclopentadienyl titanium triastatide, andthe corresponding metal halide compounds containing ethylcyclopentadienyl, butyl cyclopentadienyl, octyl cyclopentadienyl,dimethyl cyclopentadienyl, dihexyl cyclopentadienyl, vinylcyclopentadienyl, ethynyl cyclopentadienyl, phenyl cyclopentadienyl,methylphenyl cyclopentadienyl, acetyl cyclopentadienyl, allylcyclopentadienyl, benzyl cyclopentadienyl, tolyl cyclopentadienyl, andother like radicals. In addition to the aforementioned titaniumcompounds, the corresponding zirconium and hafnium compounds can also beemployed. Thus, other monocyclopentadienyl compounds are methylcyclopentadienyl zirconium trichloride, methyl cyclopentadienylzirconium tribromide, cyclopentadienyl hafnium trichloride,cyclopentadienyl hafnium tribromide and the like. Other compounds aremethyl cyclopentadienyl titanium dibutoXy chloride, cyclopentadienylzirconium methoxy dibromide, cyclopentadienyl tributoxy hafnium,dimethyl cyclopentadienyl titanium trichloride, phenyl cyclopentadienylzirconium trichloride, and the corresponding compounds of titanium,zirconium and hafnium containing butyl cyclopentadienyl, octylcyclopentadienyl, dimethyl cyclopentadienyl, dihexyl cyclopentadienyl,vinyl cyclopentadienyl, allyl cyclopentadienyl and other like radicals.Other compounds are indenyl titanium trifluoride, indenyl zirconiumtrichloride, fluorenyl titanium tribromide, fluorenyl zirconiumtrifluoride, 2-methyl-indenyl titanium trichloride, and the like. Any ofthe above compounds can be employed to plate their respective metallicsubstituent upon a multitude of substrates-employing any of thetechniques described hereinbeforeby controlling the temperature of theplating operation so that temperatures above the decompositiontemperature of the particular monocyclopentadienyl group IV-Bcoordination compound are employed.

The group IV-B metal platesparticularly titanium and zirconiumplatesfind a multitude of uses in the aircraft, missile and chemicalprocessing industries. Thus, aircraft and missile components whichrequire ultra high quality performance characteristics, such asresistance to high temperatures and to chemical attack, can satisfactorily meet these requirements when coated with a group IV-B refractory,according to the process of the instant invention. In the chemicalprocessing industry, the group IV-B metal plates produced by the processof this invention find use in equipment subjected to high temperaturesand chemical attack--as, for example, heat exchangers employed in suchan environment. A very thin film of the metal plated on varioussubstrates is sufficient for most applications. In some instances thisfilm has a thickness on the order of only a few microns. By employingthe process described herein, thicker plates can easily and economicallybe obtained-should such thickness be necessary for a particularapplication.

Another important use of the titanium plates produced herein is in thecoating of cooking utensils-particularly aluminum cooking utensils. Byvirtue of such coating food does not stick to the utensil, therebyeliminating the necessity for cooking lubricant and the like.

Another use of the metal plates produced according to the process ofthis invention is in the plating of plastics. An example of such a useis the titanium plating of automotive interior plastic trim. By virtueof such plating the serious problem encountered in automobile bodiesstored for long periods of time, whereby vapor loss from the plasticdeposits on car windows and Windshields, is simply and economicallyovercome.

We claim:

1. A process for plating a substrate with a group IV-B transition metalcomprising decomposing the vapors of a monocyclopentadienyl group IV-Btransition metal coordination compound while in contact with saidsubstrate; said compound containing, in addition to the cyclopentadienylgroup, at least one electron donor group capable of donating 1 to 4electrons.

2. A process for plating a substrate with a group IV-B transition metalcomprising heating the substrate to be plated to a temperature above thedecomposition temperature of a monocyclopentadienyl group IV-Btransition metal coordination compound, having, in addition to thecyclopentadienyl group, at least one electron donor group capable ofdonating 1 to 4 electrons, and contacting the vapors of saidcoordination compound with said heated substrate.

3. The process of claim 2 wherein said coordination compound iscyclopentadienyl titanium trichloride.

4. The process of claim 2 wherein the said coordination compound iscyclopentadienyl zirconium trichloride.

5. A process for plating a substrate with titanium which comprisesdecomposing the vapors of a monocyclopentadienyl titanium trihalidewhile in contact with said substrate.

6. A process for plating a steel substrate with titanium which comprisesdecomposing the vapors of a monocyclopentadienyl titanium trihalidewhile in contact with said substrate.

7. A process for plating an aluminum substrate with titanium whichcomprises decomposing the vapors of a monocyclopentadienyl titaniumtrihalide while in contact with said substrate.

8. A process for plating a carbonaceous substrate with a group IV-Btransition metal which comprises decomposing the vapors of amonocyclopentadienyl group IV-B transition metal trihalide while incontact with said substrate.

9. A process for plating a substrate which comprises decomposing thevapors of a monocyclopentadienyl group IV-B transition metalcoordination compound while in contact with said substrate; saidcompound containing, in addition to the cyclopentadienyl group, at leastone electron donor group selected from the group consisting of chlorine,bromine, butoxy, propoxy, ethoxy, and methoxy groups.

References Cited in the file of this patent UNITED STATES PATENTS2,508,509 Germer et al May 23, 1950 2,638,423 Davis et a1. May 12, 19532,690,980 Lander Oct. 5, 1954 2,898,235 Bullotf Aug. 4, 1959 2,955,958Brown Oct. 11, 1960

1. A PROCESS FOR PLATING A SUBSTRATE WITH A GROUP IV-B TRANSITION METALCOMPRISING DECOMPOSING THE VAPORS OF A MONOCYCLOPENTADIENYL GROUP IV-BTRANSITION METAL COORDINATION COMPOUND WHILE IN CONTACT WITH SAIDSUBSTRATE; SAID COMPOUND CONTAINING, IN ADDITION TO THE CYCLOPENTADIENYLGROUPS, AT LEAST ONE ELECTRON GROUP CAPABLE OF DONATING 1 TO 4ELECTRONS.